This invention relates generally to the treatment of sewage or waste water. More particularly, this invention relates to the treatment of sewage or waste water discharged from houses and other buildings which are not connected to a municipal sewer system such that, after the sewage has passed through the Three Stage Sewage Treatment Plant (TSSTP), it has been cleaned to a level acceptable for discharge into the environment so that it will not contaminate the ground water. Thus, the TSSTP provides an alternative to septic systems for buildings constructed outside of a local municipal sewer system.
The TSSTP expands upon existing sewage treatment technology, particularly the conventional sewage treatment technology which uses aerobic microorganisms to break down sewage. One such conventional sewage treatment device is seen in U.S. Pat. No. 5,549,818. This conventional sewage treatment device consists of a cylindrical tank which encompasses a funnel-shaped clarifier. Thus, the cylindrical tank is divided into an outer chamber, between the outer wall of the tank and the clarifier, and an inner chamber, inside the clarifier. Air is introduced into the outer chamber by multiple air droplines, which are connected to an air compressor and which pump air bubbles into the sewage in the outer chamber. Sewage flows into the outer chamber where it comes in contact with the air bubbles. The introduction of air facilitates the breakdown and digestion of the sewage by aerobic microorganisms present in the sewage. The aerated sewage then proceeds into the clarifier through an opening at the bottom of the funnel-shaped clarifier. Inside the clarifier is a quiescent zone. This area of calm in the inner chamber of the device allows for settling to occur, with the solids falling back out of the clarifier and collecting on the bottom of the treatment tank. Accordingly, the waste water becomes cleaner as it progresses upward in the funnel-shaped clarifier, continuing to allow gravity to separate the solids from the water. So, by the time the sewage has progressed up through the clarifier, it has been substantially cleaned. This treated effluent exits near the top of the clarifier and is discharged.
While conventional one-stage sewage treatment devices, such as that described in U.S. Pat. No. 5,549,818, act to substantially clean sewage, such sewage may be cleaned more thoroughly and processed more effectively by combining this aerobic cleaning process with additional stages. Initially, this was done by connecting the aerobic sewage treatment device to a separate trash tank and, sometimes, to a separate pump tank. This configuration, linking separate elements together, was cumbersome and bulky. Three separate installations were required, with each separate tank then being connected together with pipes in the field to enable sewage flow between the separate tanks. This installation process was slow and, because it essentially required a custom fitting in the field, prone to error and/or expense. Furthermore, the use of three separate devices connected by pipes meant that the complete unit was spread out, requiring extensive digging in order to clear a sufficiently large area for installation. In addition to adding cost to the installation of the unit, this extensive digging was also inconvenient to the landowner because it causes widespread damage to the yard.
In an attempt to overcome several of these problems, single units encompassing multiple stages in a single device have been constructed. One example of a multi-stage sewage treatment device is seen in U.S. Pat. No. 3,741,393. This device divides a single, plastic septic tank into three subtanks: a trash tank, an aerobic tank (although it differs substantially from the aerobic tank seen in U.S. Pat. No. 5,549,818 because it does not employ a clarifier with air droplines), and a settling tank. The use of plastic to construct the tank, however, is problematic. Plastic is not a particularly strong material, which is problematic as the device must be buried beneath the ground, enduring substantial weight over its life. And, plastic may tend to degrade over time, raising the possibility of leakage and groundwater contamination.
Other devices have attempted to overcome these problems by building a multi-stage sewage treatment unit out of concrete, a material which is very strong under compression and which does not degrade over time. Such a device may be seen in U.S. Pat. No. 4,608,157, which has a trash tank, an aerobic tank (although it, again, differs substantially from the aerobic tank seen in U.S. Pat. No. 5,549,818 because it does not employ a clarifier with air droplines), and a settling tank. The problem with concrete, however, is that it is heavy, complicating installation, and brittle. Current concrete multi-unit sewage treatment devices, such as that seen in U.S. Pat. No. 4,608,157, make use of rectangular-shaped tanks. This is not ideal, however, when the aerobic tank employs a clarifier and air droplines (which is a superior process for cleaning sewage) since it results in xe2x80x9cdead zonesxe2x80x9d in the corners of the tank, with the sewage in those zones receiving little, if any aeration. This is a substantial problem, since proper aeration is required in order for the aerobic microorganisms to function to break down the sewage.
Earlier attempts to solve this aeration problem have resulted in prototype designs which combine a cylindrical central aerobic tank with rectangular trash and settling tanks. Unfortunately, these designs have two serious, interrelated flaws which have kept them from being successful: these designs produce either a very heavy device that, while structurally sound (due to the accumulation of large amounts of concrete at the joint locations between the tanks), is heavy and difficult to handle; or, if the design attempts to lighten the device by eliminating some of the concrete at the joints, a device that is fragile and prone to brittle breakage along the joints between the tanks (raising serious environmental contamination concerns).
The Three Stage Sewage Treatment Plant (TSSTP) of the present invention solves all of these problems due to an innovative design that uses the shape of the tanks to shore up the joints between the tanks, preventing brittle breakage. The TSSTP typically combines three separate cleaning stages into a single sewage treatment device. The sewage first enters a pretreatment area, which screens large solids while allowing anaerobic microorganisms to begin breaking down the sewage. The sewage then proceeds into a cylindrical aerobic tank where it is thoroughly aerated as it traverses down the height of the tank and then clarified as it proceeds upward through the clarifier. Finally, the sewage enters a post-treatment tank, where it is chlorinated and stored for additional settling before discharge. This multi-step process produces a cleaner effluent. The three cleaning stages have been combined into a single unit for convenience and ease and installation. And, the device is constructed of concrete, such that it is strong and durable, providing a long operating life without any degradation. Finally, the TSSTP maintains a reasonable weight, again ensuring ease of installation (without the need for expensive lifting equipment), while also overcoming the longstanding problem of brittle breakage along the joints between the tanks with it uniquely shaped design.
The central aerobic tank is cylindrical, such that it has a circular cross-section that eliminates xe2x80x9cdead zones.xe2x80x9d The side tanks have an arch-shaped horizontal cross-section (when viewed from above) which provides sufficient architectural strength to prevent any brittle breakage. Thus, the TSSTP represents an improved design which overcomes existing problems in the multi-stage sewage treatment field to produce a better product. This novel design can be used to construct a concrete device with one or more side tanks of the designated shape connected to a cylindrical aerobic tank, In the TSSTP, two side tanks are used in conjunction with the a cylindrical aerobic tank in order to employ a more thorough, three stage cleaning process.
The TSSTP is a single, unitary device utilizing a three stage procedure for treating sewage. The TSSTP is comprised of a pre-treatment tank, which holds the sewage for a time while allowing the anaerobic microorganisms in the sewage to begin initially breaking down the sewage, an aerobic tank, in which the sewage is aerated to allow aerobic microorganisms to further break down the sewage and then clarified as the heavier particles separate from the effluent, and a post-treatment tank, which chlorinates the effluent before discharge. All three tanks are formed as a single, whole unit (using a concrete mold which incorporates all three tanks, creating a continuous, one-piece concrete unit with three separate tanks without the need to join separate tanks together), allowing for convenient installation.
Raw sewage enters the pre-treatment tank first to allow the anaerobic microorganisms in the sewage to begin the initial processing of the sewage. The pre-treatment tank has side walls and a bottom, and the top is sealed by a separate cover. Anaerobic microorganisms feed on the sewage, breaking it down in the process. The pre-treatment tank also serves to screen out objects which would hamper the functioning of the aerobic tank. As the pre-treatment tank continues to accept raw sewage, sewage is forced out of the pre-treatment tank through the outlet conduit. Near the top of the pre-treatment tank is a overflow conduit which leads to the aerobic tank. Gravity will segregate the sewage in the pre-treatment tank, such that light solids will float upon the surface while heavy solids will settle to the bottom. In between these two zones is a zone of effluent which is relatively free of particles. The overflow conduit drains sewage from this particle-free zone beneath the surface level, thereby screening out floating solids and heavy solids. An effluent filter, which is not required, may cover the opening of the overflow conduit to further prevent large particles from passing through the overflow conduit. In this way, the overflow conduit traps the large solid contaminants so that they do not enter the aerobic tank and clog the device. After the raw sewage has been gravity separated and processed by anaerobic microorganisms, it flows into the aerobic tank for the next stage of the treatment process.
The aerobic tank is a cylindrical vessel with sidewalls and a bottom, and the top is sealed by a separate cover. The tank encompasses a funnel-shaped clarifier. The clarifier is wide near the top of the aerobic tank and narrows towards the bottom of the tank, and there is an opening in the bottom of the clarifier. There are many methods which could be used to hold the clarifier in place inside the aerobic tank. The TSSTP uses a clarifier design with a lip that overhangs the sidewalls of the aerobic tank. Thus, the clarifier actually hangs down from the top of the sidewalls. The lip of the clarifier is held firmly in place between the top of the aerobic tank sidewalls and the cover for the aerobic tank. The funnel-shaped main body of the clarifier is offset slightly down from the top of the tank, so that there is a gap between the top of the clarifier and the top of the aerobic tank. This offset provides clearance for the air feed conduit. The clarifier hangs down inside the vessel, not reaching down to the bottom of the aerobic tank but leaving an area of clearance between the bottom of the clarifier and the bottom of the aerobic tank. Thus, the aerobic tank is divided into two chambers by the clarifier. Between the outer sidewalls of the aerobic tank and the clarifier is the outer chamber, where aeration of the sewage occurs, while the volume inside the clarifier is the inner chamber of the aerobic tank, where solid particles are gravity separated from the effluent.
Running down into the outer chamber of the aerobic tank from the top of the aerobic tank are droplines. These droplines are typically distributed in the outer chamber such that they provide for aeration throughout the upper part of the outer chamber, above the bottom of the clarifier. This placement of the droplines in the cylindrical aerobic tank ensures that there are no xe2x80x9cdead zones.xe2x80x9d These droplines are conduits which are typically capped at the bottom end and which have small holes for emitting air. The top end of these droplines are connected to an air feed conduit which directs air from the compressor, so that the droplines will emit air bubbles into the outer chamber, continuously aerating the sewage passing through the outer chamber of the aerobic tank. The inner chamber, located inside the clarifier, is screened from the aerating effect of the droplines by the walls of the clarifier, so this inner chamber is a non-turbulent, quiescent zone. Near the top of the inner chamber with its opening located inside the clarifier is an outlet drain leading to the post-treatment tank. Typically, the outlet drain is comprised of an outlet conduit, extending from the clarifier of the aerobic tank to the post-treatment tank, and a T-Baffle, which controls the flow of effluent into the outlet conduit. The T-Baffle is comprised of two T-joints. The first T-joint connects to the outlet conduit and extend upwards and downwards from the outlet conduit. The second T-joint connects to the bottom of the first T-joint, so that its two openings extend out perpendicularly from the openings of the first Tjoint. The uppermost opening of the first T-joint extends above the fluid level within the clarifier, acting as a vent for the T-Baffle. Both of the openings for the second T-joint are beneath the fluid level within the clarifier. Thus, the effluent enters the T-Baffle through the two lower openings and then flows into the outlet conduit, out of the clarifier of the aerobic tank and into the post-treatment tank. Because a film of scum can form atop the liquid in the aerobic tank, the T-Baffle acts to drain effluent from beneath the surface of the fluid to provide for a cleaner effluent discharge from the aerobic tank.
The sewage, which has already been initially processed by anaerobic microorganisms, enters the aerobic tank through the overflow conduit located near the top of the aerobic tank. The sewage moves into the outer chamber of the aerobic tank and descends downward through the outer chamber as additional sewage enters the aerobic tank through the overflow conduit. As the sewage descends, it passes through the air bubbles emitted from the drop lines. This excites the sewage, causing turbulent motion, as it aerates the sewage. Injecting air into the sewage activates and stimulates the aerobic microorganisms in the sewage. This causes the aerobic microorganisms to multiply and increases the amount of sewage that they digest. This aerobic process eliminates sewage contaminants to a great extent, cleaning the sewage. After passing through the aeration zone of the outer chamber of the aeration tank, the sewage enters a relatively calm zone below the air holes in the drop lines. Here, settling begins to occur, with heavier solids falling towards the bottom of the aerobic tank. The sewage in the quiescent zone is displaced upwards and through the opening in the bottom of the clarifier and into the inner chamber of the aerobic tank as more sewage enters the outer chamber of the aerobic tank. The sewage in the inner chamber is in a relatively calm state, and so contaminants, acted upon by gravity, will continue to settle downwards. In this way, the clarifier acts to screen out solid contaminants from the effluent. This continuous process results in a very clean effluent at the top of the inner chamber, where it is drained off by the T-Baffle and flows out of the aerobic tank through the outlet conduit and into the post-treatment tank.
While the post-treatment tank and the pre-treatment tank may be located anywhere around the aerobic tank, the post-treatment tank is generally located on the opposite side of the aerobic tank from the pre-treatment tank. It has sidewalls and a bottom, and the top is sealed with a separate cover. The outlet conduit enters the post-treatment tank near the top of the tank. There, it may connect to a chlorinator, through which the effluent passes into the storage space of the post-treatment tank. When passing through the chlorinator, the effluent is chlorinated, generally by flowing across a chlorine tablet. The cleaned effluent is held in the post-treatment tank, allowing further settling and diffusion of the chlorine throughout the effluent. When the effluent rises to a certain level, it activates a float switch, triggering a pump, which can be either internal or external, discharging the cleaned effluent.
The TSSTP is formed such that the pre-treatment tank and the post-treatment tank connect to the aerobic tank, creating a single unit which performs the three stage cleaning process. The top of the three tanks are capped to make the TSSTP a closed system. While several individual covers may be used, it is preferable to use a single cover for the entire TSSTP device, as this provides additional strength and rigidity to the device. This single cover needs to be formed so that it seals each tank individually, so that there can be no sewage gas transfer between the tanks. In addition, chlorine cannot be allowed to flow from the post-treatment tank to the aerobic tank, as that would kill the aerobic microorganisms which are crucial to the cleaning process. The portion of the cover for each tank may have a service hatch for maintenance. Generally, there is a riser extending from the top of the aerobic tank, allowing for inspection and cleaning of the aerobic tank. Also, there is generally a larger high riser on the post-treatment tank, large enough to allow for installation of an internal pump in the post-treatment tank, with a loose fitting cap that allows for venting of air from the system. It is also through this riser that an external pump would operate.
The TSSTP is typically constructed of wire reenforced concrete, which is both strong under compression and non-degradable To reduce the weight of this concrete device as much as possible while maintaining strength and durability, the TSSTP employs a uniquely shaped design. The central aerobic tank is cylindrical, such that in plan view it is circular in cross-section. Both the pretreatment tank and the post-treatment tank have an arch-shaped (or crescent-shaped) plan view horizontal cross-section (which extends along the height of the cylindrical aerobic tank to form a three dimensional tank), and are connected to the aerobic tank such that the two approximately parallel sidewalls of each tank, which extend from the semi-circular arc of the cross-section, attach tangentially to the outer cylindrical walls of the aerobic tank (such that the outer wall of the aerobic tank forms the final wall closing the tank). Thus, both the pre-treatment tank and the post-treatment tank each have a semi-circular wall (farthest away from the aerobic tank), two approximately parallel side walls, and a connecting wall (which is shared with the aerobic tank). The semi-circles which form the curved portion of the arched cross-sections of the pre-treatment and post-treatment tanks have approximately the same radius as the circular cross-section of the cylindrical aerobic tank. The thickness of the walls for all of the tanks may be identical. All of these elements combine to form a strong unitary structure with a smooth, continuous outer wall of uniform thickness (with the outer wall of the TSSTP shaped essentially like a racetrack in the most typical formation, which has the pre-treatment tank attached to the aerobic tank directly opposite from the post-treatment tank, which is attached to the other side of the aerobic tank) that uses the circular elements of the design to take advantage of the strength of concrete in compression. The inherent strength of this shape eliminates the need for excess concrete buildup at the joints (thereby reducing the weight of the device, and making it much more practicable to install), while providing for strong joints linking the pre-treatment tank and the post-treatment tank to the central aerobic tank. And, the smooth profile of the device also reduces the possibility of damage to the device during installation.
Generally, the tanks are sized so that they do not have to be pumped clean very often, on average requiring cleaning once a decade. In addition, the sizes of the tanks are dependant upon the expected amount of sewage generated by the buildings they service on a daily basis. The aerobic tank must also be sized so that the sewage remains in it long enough for the aerobic microorganisms to effectively process the sewage. The TSSTP is typically installed below ground, buried in the yard of a residence, so its compact design simplifies installation and minimizes the amount of damage to the yard. And, of course, the device must be able to withstand the weight of the soil under which the device is buried.
It is an object of this invention to clean sewage in preparation for discharge. In doing so, this invention captures large solids in the pre-treatment tank, uses both anaerobic and aerobic processes to break down the sewage, separates the contaminants from the sewage water, and chlorinates the effluent. It is still another object of this invention for it to be easy-to-install, relatively lightweight, strong, and durable, requiring very little maintenance. It is yet another object of this invention to provide a three stage sewage cleaning process in a single, compact concrete unit. It is yet another object of this invention to utilize a design shape which allows for a structurally sound unitary device with a cylindrical aerobic tank and connected side tanks. It is yet another object of this invention to discharge water which meets or exceeds state and federal water quality requirements. It is yet another object of this invention to allow for inspection of the tanks and to allow for cleaning and maintenance of the invention.